Circuits for modifying potentials



July 31, 1951 l. J, P. JAMES CIRCUITS FOR MODIFYING POTENTIALS Original Filed Nov. 28, 1945 INVENTOR [Vzzlioe Jaim Pezl'ozmd James Patented July 31, 1951 ,i

CIRCUITS FOR MODIFYING POTENTIALS Ivanhoe John Penfoundl'James, Ealing, London,

England, assigner to Electric and Musical vIndustries, Limited, a British corporation l originati application November 2s, 1945, serial No. 631,436. Divided and thisapplication February 11, 1949, Serial No. 75,943. In Great Britain January 12, 1944 f8 Claims. (Cl. Z50-27) This application is a division of application Serial No. 631,436, filed November 28, 1945, in the names of Eric Lawrence Casling White, Ivanhoe John Penfound James, and John Edward Best, and entitled Circuits for Modifying Potentials. The claims of this application are directed to the subject matter illustrated in Figs. 2 and 3 of the drawing.

This invention relates to electric circuits for modifying electric potentials. More particularly the invention relates to circuits for deriving from a first and given potential a second potential which is mathematically related to the first potential in integral or derivative manner with respect to time. In one aspect the invention relates to the generation of electrical variations of sawtooth character.

Circuits for so modifying a given potential that the modified potential stands to the given potential in the relation of the mathematical integral or derivative with respect to time of the given potential are well known. For example, if a given potential is applied to a circuit consisting simply of a resistance and a capacity in series itis possible to derive from the circuit a modied potential which is related with accuracy to the mathematical integral or derivative of the given potential, providing that the modified potential is always small compared with the given potential, or that the frequencies of effective Fourier components of the given potential lie within a certain frequency range determined by the constants of the circuit. It is often desirable to obtain a greater amplitude of modified potential or a wider range of operating frequencies. The object of the present invention is to provide improved circuits whereby these ends may be achieved According to the present invention, there is provided an electric circuit arrangement for modifying a given potential comprising a source its other end to said point whereby the current in said impedance due to said potential is determined substantially only by said given potential and saidV impedance, there being included in the circuit of said amplier a second impedance 2 which in said effective operating frequency range is large compared with the impedance provided by said amplifier at said point and of diierent electrical nature from said first impedance, the arrangement being such that the whole or a fixed proportion of said current ows in said second impedance and a potential modied coinpared with said given potential is developed dependent substantially only on said current and said second impedance.

' In order that the said invention may be clearly understood and readily carried into effect, it will now be more fully described with reference to the accompanying drawings in which:

Figures l to 3 illustrate some embodiments of the invention diagrammatically. In these drawings like reference numerals indicate like elements.

Figure 1, whichis claimed in Serial No. 631,436, shows a circuit arrangement for modifying potentials in a predetermined manner. The source, not shown, of these potentials is connected to terminal I0 so as to develop said potentials thereat. Potentials modiiied in the required manner are developed at terminal ll. Thermonic valves I2 and I3 together with their circuit connections including the coupling elements I5, I6, Il and I9 constitute said thermionic amplifier aforementioned and the circuit elements 2D and 2I said first and second impedances, respectively. In said thermionic amplifier the valve I2 is arranged to develop a large gain between itsv anode and its control grid I4. Potentials are developed at the anode of valve I2 by means of the anode circuit impedance I5 which may be a resistance and are transferred by means of the coupling circuit I6, I'I to the control grid I8 of valve I3. Impedance elements I 6 and Il may be resistances and the end of resistance I'I not connected to controlgrid I8 will then be connected to a point of fixed and suiiiciently negative potential to bring said control grid to a proper operating potential. The anode of valve I3 is connected directly to a point of xed positive potential while the cathode of said valve is connected by means of the large resistance I9 to a point of iixed negative potential so that potential variations occurring at said cathode are substantially identical with those applied to the control grid I8. If it is desired that the operating range of frequencies of said amplifier should include those at which stray capacities affect the gain of the amplifier, known methods may be employed for extending the amrilier response. A

It will be seen that the impedance 2| constitutes termine the required form of the potential devel` oped at terminal II in relation to Vthe potential l applied at terminal I Il. They suflce to determiner the desired relationship by virtuepf the"li`gh degree of degeneration presentY inthe eircuitf,

Since the feedback connection to the input of the amplifier, namely to the controlgrid I4, is of shunt character, the input impedance of the amplifier, that is, the impedance presented to impedance element 20, is reduced by the feedback at least in a certain range of frequencies to a lou1 value. For all frequencies therefor for Which the impedance of element'20 is large `comparedwith said input impedance the current Yfiuowf ing in element 2D will depend only on the impedance of this impedance element and onthe poten.- tial applied at the terminal I0. If ZiUfw) repre;- sents this impedance and U the applied poten? tial, said current will be represented by U/Z1(7'w). This current must necessarily flow in the imped; ance element 2| and, if this impedance'is` sulifciently large, will set up potential variations thereby large compared with those occurring; at the grid I4 of the valve I2 which by reason of said 10W value of impedance thereat are cf small magnitude. If the output potential thus set up at the cathode ofvalve I3 be represented by Vand the impedance of impedance element 2I be represented by Zm'w), V will be related to thel poten: tial U according to 1 zzc'wr met) zal?)Y a Y V zien) (n) where D represents the differential operator: i dt The operator Z2(D) /Z 1'(D) represents the-desired predetermined relation between the potential' a'p'- plied to the circuit at terminal I0 andthat derived at terminal I I. Means for applying the proper biasing-poten.-

tial to the control grid of valve I 2" have notV been described but any known and suitable means may be employed. If impedance 2| is a'simpleresist.- s

ance and impedance 20 a simple 4capacity,itlis sufficient to bring the cathode of valve1|3 tothe necessary biasing potential: "With ,thisar'range- 11e-'scarf time@ say Thus with this arrangement V is the time derivative of U and the circuit is a differentiating circuit. If the impedance 2I is a capacity and impedance 20 is a resistance, then the relation between V and U is of the form 1 VTRCDU that is 1 V--fUdt and the circuit is an integrating circuit. Other .forms of impedance elements may be used in the circuit for impedances 20 and 2I. As has been stated, however, they must always be of electrically' different nature, that is to say the impedance functions ZiUw) and ZzUw) must be different. With such other forms the circuit can be made to modify or shape an applied potential in other ways than those just described by way of illustration'.

Figure 2 shows an arrangement according to the present invention in which a diiierent form of amplifier is employed. The amplifier comprises the ampliiier valve 30 having its control grid 3I connected to ground and cathode connected to a point of fixed negative potential by means of resistance 32. The input terminal I0 is connected to the cathode of valve30 through impedance 20 which may be a capacity as indicated while the output terminal is connected to the anode of valve 38 at which potentials are developed in response to potentials applied to termina-l I0 by virtue of impedance 2l which may be a resistance connected in the anode circuit of valve 30. The impedance 32 is made sufficiently large for the circuitv to be highly degenerative and to present at the cathode of valve 30 and to impedance 2l) an impedance of small magnitude substantially equalto or comparable with the reciprocal of the mutual conductance of valve 38. Provided impedance 2U is large compared with the impedance presented to it at said cathode, the current in impedance 20 is determined solely by the magnitu'deY of said impedance and the potential applied vto terminal I0. This" current efectively'divides between the two branches formed bythe impedance 32 and the'valv'e 30. The latter branch effectively' presents a very' low impedance compared with 'that of the formerand substantially thewhole of the current owing'in impedance 20 is diverted into said latter branch. vOf thisA a rproportion will flow in the screen grid circuit :of valve 3 0 b ut a major portion will now in theanode circuit of the Valve and thus in impedance ZL The'valve 30 may be operated so that theseprO- portions remain fixed `and this 4being the ase vthe relation between input'and Voutput potentials may be written l i K ZD) f zum (v3) where K is the proportion of current flowing in the anode circuit, this relationholding ysubject .to the condition that there are no frequencies effectively present in thepotential U'for which the impedance of impedance element 20 is not large compared with the impedance presented to it Vat the cathode of valvel'30. As before, Z(9`w) and Zzty'w) represent the inipedancesfof impedance elements'20`and `I respectively atffrequency al.' If the valve 3Dis replacedbya'triode the proportionfKbecomes unityQ The.effectifci 'ascreen 'within the valve"is"still"obtainedin this case, since as the control grid 3l is earthed it acts as a screen between the input and output circuits of valve 3B. As shown in Figure 3, if desired the impedance 2l may be inserted in the screen lead of valve 39 instead of the anode lead in which case the output terminal ll will be connected to the screen electrode of valve 39. If necessary grid 3l may be used for mixing additional potentials to the output potentials. The circuit as shown is a diierentiating circuit.

It is to be noted that in all of the abovedescribed embodiments of the invention the source of the given potentials is assumed to be connected between the terminal Ill and a point of xed potential which point is conveniently ground as indicated in the drawings.

What is claimed is:

1. A wave shaping circuit for changing the wave shape of a voltage applied thereto, said circuit comprising a vacuum tube having a cathode, a control grid and an output electrode, a cathode resistor connected in the cathode circuit of said tube, one end of said resistor being connected to said cathode, a rst impedance unit, one end of which is connected to said cathode and the other end of which has said voltage applied thereto, said control grid being connected to a point of constant potential such as ground, a second impedance unit connected to said output electrode and through which at least a substantial portion of the tube space current flows, means for applying a positive operating potential to said output electrode, said second impedance unit being of a different electrical nature than said first impedance unit, and output terminals to which are applied the reshaped Voltage appearing across said second impedance unit.

2. The invention according to claim 1 wherein said output electrode is an anode.

3. The invention according to claim 1 wherein said output electrode is a screen grid.

4. The invention accordingto claim 1 wherein said first impedance unit has an impedance that is large compared with the impedance presented to it at said cathode.

5. A wave shaping circuit for changing the wave shape of a voltage applied thereto, said circuit comprising a vacuum tube having a cathode, a control grid Land an anode, a cathode resistor connected between said cathode and a source of negative bias, a first impedance unit, one end of which is connected to said cathode and the other end of which has said voltage applied thereto, said control grid being connected to a point of constant potential such as ground, a second impedance unit connected to said anode and through which the cathode-anode current of said tube ows, ymeans for applying a positive operating potential to said anode, said second impedance unit being of a different electrical nature than said first impedance unit, and output terminals to which are applied the reshaped voltage appearing across said second impedance unit.

6. Av wave shaping circuit for changing the Wave shape of a voltage applied thereto, said circuit comprising a vacuum tube having a cathode, a control grid and an anode, a cathode resistor connected between said cathode and a source of negative bias, a rst impedance unit, one end of which is connected to said cathode and the other end of which has said voltage applied thereto, said control grid being connected to a point of constant potential such as ground, a second impedance unit connected to said anode and through which a positive operating potential is applied to said anode, said second impedance unit being of a dilerential electrical nature than said rst impedance unit, and output terminals to which are applied the reshaped voltage appearing across said second impedance unit.

7. A wave shaping circuit for changing the Wave shape of a voltage applied thereto, said circuit comprising a vacuum tube having a cathode, a control grid and an anode, a cathode resistor connected between said cathode and a source of negative bias, said cathode resistor having suiciently high impedance to make said circuit highly degenerative, a first impedance unit, one end of which is connected to said cathode and the other end of which has said voltage applied thereto, said control grid being connected` to a point of constant potential such as ground, a second impedance unit connected to said anode and through which at least a substantial portion of the tube space current flows, means for applying a positive operating potential to said anode, said second impedance unit being of a different electrical nature than said rst impedance unit, said iirst Aimpedance unit having an impedance that is large are applied the reshaped voltage appearing across said second impedance unit.

8. A differentiating circuit for changing the wave shape of a voltage applied thereto, said circuit comprising a vacuum tube vhaving a cathode, a control grid and an anode, a cathode resistor connected between said cathode and a source of negative bias, a capacitor, one end of which is connected to said cathode and the other end of which has said voltage applied thereto, said control grid being connected to a point of constant potential such as ground, a resistor connected to said anode and through which a positive operating potential is applied to said anode, said capacitor having an impedance that is large compared with the impedance presented to it at said cathode, and routput terminals to which are applied the reshaped voltage appearingV across said resistor.

IVANHOE JOHN PENFOUND JAMES.

REFERENCES CITED The following references are of record in the le of this patent: f

UNITED STATES PATENTS Number Name Date 2,324,797 Norton July 20, 1943 2,412,485 Whiteley Dec. 10, 1946 

